1. Field of the Invention
The present invention relates to an organic electroluminescent device and an organic electroluminescent display device. More particularly it relates to an organic electroluminescent device which is suitable as a light-emitting element in a display device such as an organic electroluminescent display device and the like, and an organic electroluminescent display device.
2. Description of the Related Art
In recent years, in association with advanced information, needs for low-profile, low power consumption and lightweight flat-panel displays (FPD) are increasing. Particularly, organic electroluminescent display devices (hereinafter, also referred to as a “organic EL display”), which can be driven at a low voltage and can realize the display with high luminance attracts attention. Particularly, the luminous efficiency of an organic electroluminescent device (hereinafter, also referred to as a “organic EL device”) using organic light-emitting materials as a light-emitting element is significantly improved by recent research and development, and commercialization of the organic EL display including such an EL device are starting.
As the light-emitting material used for the organic EL device, generally, small molecular light-emitting materials or high molecular light-emitting polymer material, which comprises organic compounds and/or organic metal compounds. The common organic EL device using light-emitting polymer materials has, for example, a constitution in which an anode made of indium tin oxide (ITO) or the like, a hole transport layer (PEDOT-PSS (poly(ethylenedioxythiophene)/poly(styrene sulfonate)), a light-emitting layer formed containing the light-emitting polymer material, and a cathode made of Ca/Al are formed on a glass substrate in turn. It has been reported that the organic EL device having such a constitution has relatively excellent luminance, luminous efficiency (power consumption) and lifetime. However, common organic EL devices are not adequate as far as the luminance, the luminous efficiency (power consumption) and particularly the lifetime in consideration of the application range to actual commodity products, and their application is limited.
Thus, in order to improve the characteristics, particularly, the luminance, the luminous efficiency and the lifetime, of the organic EL device, various measures are hitherto studied. For example, technology of improving the light-emitting material itself (for example, Patent Document 1), and technology for improving the cathode (for example, Non-patent Document 1) are proposed. However, in order to attain a practical organic EL device having wide applications, the above-mentioned measures were inadequate. For example, the organic EL display device is extremely inferior in power consumption and lifetime to the FPD using a liquid crystal display panel even when the above-mentioned measures are taken.
On the other hand, technology of blending a polymer containing at least two emissive polymers in a polymer film (light-emitting layer) is disclosed (for example, Patent Document 2). However, this technology is a method of obtaining different colors by controlling a voltage and is not a method of improving the luminance, the luminous efficiency and the lifetime of the organic EL device.
Patent Document 1: National Publication of International Patent Application No. H11-508731
Patent Document 2: National Publication of International Patent Application No. H10-500441
Non-patent Document 1: Y. Cao, Gang Yu, I. Parker and J. Heeger, “Ultrathin Layer Alkaline Earth Metals As Stable Electron-Injecting Electrodes For Polymer Light Emitting Diodes”, Journal of Applied Physics, (USA), 2000, Vol. 88, p. 3618